New York documentarian Paul Sahner's blog NYC Grid is a lovely project, and amongst the coolest recurring features on the site is Before & After, which compares archival images of New York monuments with photos of the same spot today. Above, we see the entrance to the Manhattan Bridge as it was in 1915, compared with the monster in 2013.

Many of the photos on these pages are equipped with an interactive slider that lets you transition between the before and after photos. (We've experimented with this concept before.) The effect is pretty spectacular, and it's particularly stirring because Sahner does such a lovely job matching the photos up perfectly. Check it out. [NYC Grid via Gothamist]